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Biomedical subjects

J R Thompson

Publications and source records attributed to J R Thompson.

At least 235 records · Page 13Linked to original sources
PubMed1986

Abnormal function of the temporomandibular joints and related musculature. Orthodontic implications. Part II.

Timing of mandibular growth and orthodontic treatment are coincidental, not cause-and-effect. Comparison of cephalometric radiographic tracings made before, during, and after treatment has shown no evidence that orthodontic forces can either arrest or stimulate growth of the condyle. Conversely, the growth behavior of the condyles can have a profound effect on the time required to achieve an orthodontic correction and on the anatomic and functional relationships at the end of treatment and later. Mandibular growth at the moment of orthodontic force application can have important effects on facial growth and function. If there is no growth, the mandible may rotate downward and backward, and condyle displacement and clicking can occur. Future growth rarely leads to recovery of such alterations. With adequate growth at the moment of orthodontic force application, the freeway space is maintained and horizontal tooth movement does not alter mandibular position. The position of the maxillary incisors in the face must be based on many considerations going far beyond arbitrary conformity to some "standard" values based on averages. Functional relationships and their effects on the joints are one of those considerations, along with esthetics. Dynamic thinking requires that maxillary incisors not be over-retracted, anticipating continued growth of the condyle that can reposition the body of the mandible and lower incisors downward and forward. This can occur before, during, or many years after treatment. If a tight incisor relationship is established, or develops naturally, in the early or midteens, and the condyles later outgrow the maxilla, clicking may well develop. Anterior translation of the mandible with the new growth is impeded by the incisors, so posterior displacement of the condyles occurs instead. This is most likely to occur in straight ("good") faces. Facial morphology, or pattern, has an impact on function. In the straight facial pattern, these problems usually involve incisor interference. In convex faces, the problems more often involve vertical molar interferences. Each of these presents its own unique problems and treatment requirements.

Adolescent↗
PubMed1986

Mathematical model for human myeloma relating growth kinetics and drug resistance.

We present a computer-based mathematical model that can simulate characteristic features of the clinical time course of human myeloma. It asserts that therapy resistance in myeloma cells is an inherited trait associated with the longer inter-mitotic times of some cells and that the strength of this trait affects tumour growth characteristics. These kinetic differences within the malignant cell clone may also influence therapeutic efficacy. In the model, the same total therapy, administered in different time-dose fractions, could be 'curative' or 'minimally effective' depending on kinetic properties. For example, as others have shown, in myeloma pulsed intermittent therapy is often more effective than low dose continuous therapy. According to our model this finding is compatible with a high coefficient of inheritability of resistance from one cell generation to the next. The model also suggests that if there are subclones of varying resistance, a therapy must have some effect on each of them if it is to be employed in a curative fashion. While many aspects of the model are not yet clinically testable, exploration of its concepts might increase knowledge about fundamental neoplastic mechanisms.

Antineoplastic Agents↗
PubMed1986

Intra- and inter-observer variability and accuracy in the determination of linear and angular measurements in computed tomography. An in vitro and in situ study of human mandibles.

The observer variability and accuracy of linear and angular computed tomography (CT) software measurements in the transaxial plane were investigated for the temporomandibular joint with the General Electric 8800 CT/N Scanner. A dried and measured human mandible was embedded in plastic and scanned in vitro. Sixteen observers participated in the study. The following measurements were tested: inter- and extra-condylar distances, transverse condylar dimension, condylar angulation, and the plastic base of the specimen. Three frozen cadaveric heads were similarly scanned and measured in situ. Intra- and inter-observer variabilities were lowest for the specimen base and highest for condylar angulation. Neuroradiologists had the lowest variability as a group, and radiology residents and paramedical personnel had the highest, but the differences were small. No significant difference was found between CT and macroscopic measurement of the mandible. In situ measurement by CT of condyles with structural changes in the transaxial plane was, however, subject to substantial error. It was concluded that transaxial linear measurements of the condylar processes free of significant structural changes had an error and an accuracy well within acceptable limits. The error for angular measurements was significantly greater than the error for linear measurements.

Child↗
PubMed1986

Comparison of cerebral blood flow measurements by xenon computed tomography and dynamic brain scintigraphy in clinically brain dead children.

Because of the controversy over applying adult clinical and laboratory criteria to children suspected of brain death, xenon computed tomographic cerebral blood flow (XeCTCBF) and near simultaneous scintigraphy were studied in 10 children. Six met the clinical criteria, one of whom had three indeterminate scintigrams with only central flow on XeCTCBF. Another had considerable flow with scintigraphy and XeCTCBF. One with clinical and autopsy brainstem death but preserved cortical function also had flow on both. This preliminary study establishes that brain scintigraphy is occasionally hypersensitive to insufficient cerebral flow and promises more accurate early assessment with XeCTCBF. The expectation is that XeCTCBF can refine the criteria for the earlier establishment of brain death.

Brain↗
PubMed1986

Time course changes in blood metabolites during endotoxin fever in sheep.

Time course changes in the concentration of plasma amino acids, glucose, insulin, and creatinine were measured in seven mature sheep during fever induced by Escherichia coli (serotype 055:B5) endotoxin. Rectal temperature was increased above that recorded in control animals from 0.75 to 6.25 h postinjection with a maximum rise of 2.3 degrees C. Total amino acid concentrations decreased (P less than 0.05) 4.5 h postinjection and remained depressed (P less than 0.05) until 19 h postinjection. The plasma concentration of each individual amino acid decreased (P less than 0.05) at some point during the experiment with the exception of tryptophan and tyrosine. Glucose concentration decreased (P less than 0.05) and remained depressed until at least 55 h postinjection. Plasma insulin concentration was elevated (P less than 0.05) from 4.5 to 13 h postinjection. Plasma creatinine concentration increased during fever (P less than 0.05) and returned to normal by 31 h postinjection.

Amino Acids↗
PubMed1986

Adenomyosis of the uterus: an enigma.

Adenomyosis has been an entity of some interest for many years, but little is known today of its pathogenesis. There is almost universal agreement that it is associated with an accentuation of the myometrial muscle pattern, multiparity, and endometrial hyperplasia. Some authors suggest that the myometrium is vulnerable to invasion by endometrial hyperplasia. Others postulate that the myometrium is vulnerable to invasion by endometrial glands because of the absence of a basement membrane. Women in the fourth and fifth decades of life are most commonly afflicted. Preoperative diagnosis is not common.

Adult↗
PubMed1986

Blood flow distribution in hind limb bones and joint cartilage from young growing pigs.

Blood flow distribution was studied in hind limb bones and joint cartilage from four ten week old and four 20 week old pigs using 141Ce-microspheres. In general, blood flow rate was greater in the epiphyseal and metaphyseal cancellous bone than in the cortical bone and joint cartilage. In the epiphyseal cancellous bone, blood flow rate was three to tenfold greater (P less than 0.01) in the surface 2 mm layer than in the remaining deeper bone in all femoral and tibial samples examined. In the joint cartilage, blood flow rate in the femoral condyle was greater (P less than 0.05) than in the proximal femur, patella, central tarsus and metatarsus in ten week old pigs, and was greater (P less than 0.05) in the femoral condyle than in the patella and metatarsus in 20 week old pigs. A significant (P less than 0.05) age-associated decrease in the rate of blood flow was observed in the femoral, patellar and metatarsal cartilage. Within the femoral condyle, no differences in blood flow were found between areas associated with relatively high versus relatively low incidences of osteochondrosis.

Age Factors↗
PubMed1986

Distribution of glycosaminoglycans and the nonreducible collagen crosslink, pyridinoline in porcine menisci.

Glycosaminoglycans and the nonreducible collagen crosslink, pyridinoline were determined in stifle joint menisci from adolescent pigs. Medial and lateral menisci were dissected into two portions, the inner third (zone 1) and the remaining two thirds (zone 2) at three different regions; anterior, central and posterior regions. Both glycosaminoglycan and pyridinoline concentrations were greater (P less than 0.05) in zone 1 than in zone 2 in both the medial and lateral menisci. In zone 1, the anterior region had a greater (P less than 0.05) glycosaminoglycan concentration than did the central and posterior regions. Light microscopic observations indicated zonal variations in collagen fiber arrangement.

Amino Acids↗
PubMed1986

A computerized analysis of astigmatism after cataract surgery.

We have performed a computerized analysis of postoperative changes in corneal astigmatism in 203 consecutive cases of extracapsular cataract extraction with posterior chamber intraocular lens implantation performed by one surgeon. Surgical technique was standardized consisting of a 140 degree posterior limbal incision with preplaced 9-0 silk and postplaced 10-0 nylon sutures. The average postoperative astigmatism was 1.60 D and the average surgically induced change in astigmatism 0.51 D after a mean follow-up of 5.4 months. When the axis of astigmatism was considered, cataract surgery on the average initially induced 2.2 D of with-the-rule astigmatism which gradually declined, stabilizing at 0.35 D against-the-rule 19 weeks postoperatively. An analysis of the natural history of astigmatism after cataract surgery helps to optimize the timing of spectacle prescription and postoperative intervention to correct excessive astigmatism. A computerized astigmatism analysis also provides rapid feedback to guide changes in surgical technique to minimize astigmatism.

Astigmatism↗
PubMed1985

Normal frontal lobe gray matter-white matter CT volume ratio in children.

We attempted to establish a computed tomographic value representing the normal volume ratio of gray matter to white matter (G/W) in children in order to have a baseline for studying various developmental disorders such as white matter hypoplasia. The records of 150 children 16 years of age or younger who had normal cranial computed tomography were reviewed. From these a group of 119 were excluded for various reasons. The remaining 31 were presumed to have normal brains. Using the region of interest function for tracing gray and white matter boundaries, superior and ventral to the foramen of Munro area, measurements were determined for consecutive adjacent frontal slices. Volumes were then calculated for both gray and white matter. A volume ratio of 2.010 (sigma = 0.349), G/W, was then derived from each of 31 children. The clinical value of this ratio will be determined by future investigation.

Adolescent↗
PubMed1985

The cerebellopontine angle and internal auditory canal: neurovascular anatomy on gas CT cisternograms.

We reviewed 103 normal gas CT cisternograms to delineate the appearance of normal neurovascular structures in the cerebellopontine angle (CPA) and internal auditory canal (IAC). Cranial nerves VII and VIII were identified in the CPA in 97% of cases, either separately (53%) or as a bundle (44%). Intracanalicular branches of the VIIIth cranial nerve were identified in 20% of cases, and cranial nerve V was visualized in the CPA in 14%. The characteristic vascular loop, usually the anterior inferior cerebellar artery, was visible in 35% of cases, and, in 22% of visualized cases, was in an intracanalicular location. The internal auditory artery was questionably visualized in one case. In 10% of cases, greater than 66% of the IAC was occupied by the neurovascular bundle. Familiarity with the normal anatomy and variants seen on gas CT cisternograms is necessary to prevent false-positive interpretations.

Cerebellopontine Angle↗
PubMed1985

Dislocation of the temporomandibular joint meniscus: contrast arthrography vs. computed tomography.

A prospective study to determine the accuracy of computed tomography (CT) for the diagnosis of dislocation of the temporomandibular joint (TMJ) meniscus was made by performing both CT and contrast arthrography on 18 joints suspected of meniscus dislocation. Arthrography rather than surgery was chosen as the quality standard for comparing CT findings, as not all patients undergoing the studies underwent surgery. The CT protocol included scanning with both closed- and open-mouth series, 1.5-mm-thick slices, soft-tissue and bone-detail settings, and coronal and sagittal reformations. Arthrography was done with linear tomography, after both lower and upper compartmental injections under fluoroscopic control. The results of each test were reported independently by the radiologist who obtained either all of the arthrograms or all of the CT scans. For dislocation of the meniscus, there was excellent agreement between the two methods. Nine menisci were dislocated according to both arthrography and CT. One meniscus was thought to be dislocated by CT, but this was not confirmed with arthrography. CT seems to be nearly as accurate as arthrography for showing meniscus dislocation, is performed with lower x-ray exposure, and is noninvasive. Arthrography discloses more detailed information about the joint meniscus, such as perforation and maceration, and should continue to be used when this kind of information is clinically important.

Adult↗
PubMed1985

Cartilage proteoglycans from normal and osteochondrotic porcine joints.

Modern pigs grow fast but are highly susceptible to degenerative joint abnormalities, including osteochondrosis. Normal and osteochondrotic humeri and femurs were obtained from five normal and ten lame adolescent boars to study cartilage proteoglycans. Histological examination of joints indicated a locally-reduced intensity of proteoglycan staining by safranin-O in lesion areas of cartilage. Cartilage proteoglycans extracted with 4.0 M guanidinium chloride were studied using Sepharose 2B gel chromatography. The proteoglycans from severely osteochondrotic joints were less (P less than 0.05) aggregated and contained a greater (P less than 0.05) proportion of smaller monomers than those from normal joints. Loss or damage of core protein, including its hyaluronic acid-binding regions, may account for the greater proportion of small monomers. The results also indicated that the proportion of hyaluronic acid in the total glycosaminoglycan uronic acid fraction, estimated by Sephadex G-200 chromatography and cellulose acetate electrophoresis, was lower (P less than 0.05) for the extracted proteoglycans than for the residual or the whole cartilage proteoglycans in all joints studied.

Animals↗